1. Field of Invention
The present invention relates to an engine having a variable valve timing device that improves the entire energy consumption efficiency and output by variably controlling the lift timing of an intake valve into advance, middle, and delay states.
2. Description of Related Art
Internal combustion engines generate power by receiving and burning air and fuel in a combustion chamber. When air is sucked, an intake valve is operated by a camshaft and air is sucked into the combustion chamber while the intake valve is open. Further, an exhaust valve is operated by the camshaft, and air is discharged from the combustion chamber while the exhaust valve is open.
However, the optimum opening/closing timings and the open time of the intake valve/exhaust valve depend on the operation conditions such as the RPM or the load of the engine. That is, the appropriate timings for lifting or opening/closing the valves depend on the RPM of the engine.
Technologies of advancing or delaying the lift timing of valves have been proposed, but it is difficult to close an intake valve early, although the lift of the valve is small under a small load at a low speed. Further, it is difficult to close an intake valve late, although the lift of the valve is large under a small load at a high speed.
FIG. 6 is a graph showing a lift of a valve through a variable valve timing device. Referring to FIG. 6, an intake valve is retarded in a starting mode and a high speed/high load mode, and the intake valve is advanced in a low speed/low load mode. Meanwhile, it is impossible to further retard the intake valve in a high speed/high load condition and a low speed/low load condition.
The information disclosed in this Background section is only for enhancement of understanding of the general background of the invention and should not be taken as an acknowledgement or any form of suggestion that this information forms the prior art already known to a person skilled in the art.